Hydrocarbons

Carbon: normally forms four covalent bonds and has no unshared pairs of electrons. Hydrogen: forms one covalent bond and no unshared pairs of electrons. Nitrogen: normally forms three covalent bonds and has one unshared pair of electrons. Oxygen: normally forms two covalent bonds and has two unshared pairs of electrons. Halogen: normally forms one covalent bond and has three unshared pairs of electrons. C H N . . . . . O = . . . . . Cl . .

Hydrocarbons Large family of organic compounds Composed of only carbon and hydrogen Saturated hydrocarbons Alkanes Unsaturated hydrocarbons Alkenes, Alkynes & Aromatics C - C C = C C C

Alkanes

Expanded structural formula: Methane Tetrahedral Expanded structural formula: showing each bond line. CH4 Molecular formula

Ethane C2H6 Molecular formula Expanded structural formula CH3 – CH3 Condensed structural formula: with each carbon atom and its attached hydrogen atoms.

Alkanes CnH2n+2 n: number of carbon atoms

Naming of Alkanes CnH2n+2 Prefix + ane

Line-angle Formula Propane CH3-CH2-CH3 Butane CH3-CH2-CH2-CH3 Pentane CH3-CH2-CH2-CH2-CH3

Naming Substituents In the IUPAC system: Removing a H from an alkane is called alkyl group. -ane Halogen atoms are named as halo. -ine -yl -O -OH Hydroxyl -NO2 Nitro

Give the name of: CH3  CH3─CH─CH2─CH3 STEP 1 Longest chain is butane. STEP 2 Number chain. CH3 CH3─CH─CH─CH3 1 2 3 4 STEP 3 Locate substituents and name. 2-Methylbutane

Give the name of: CH3 CH3   CH3─CH─CH─CH3 STEP 1 Longest chain is butane. STEP 2 Number chain. CH3 CH3   1 2 3 4 STEP 3 Locate substituents and name. 2,3-dimethylbutane

Cl CH3   CH3─CH2─CH─CH─CH3 STEP 1 Longest chain is pentane. STEP 2 Number chain from end nearest substituent. Cl CH3   CH3─CH2─CH─CH─CH3 5 4 3 2 1 STEP 3 Locate substituents and name alphabetically. 3-chloro-2-methylpentane

CH3 CH3 | | CH3─CH─CH2 ─CH─CH3 2,4-dimethylpentane 1 2 3 4 5 Cl CH3 CH3─CH2─CH─CH2─C─CH2─CH3 | Cl 7 6 5 4 3 2 1 3,5-dichloro-3-methylheptane

Br  CH3─CH─CH2─CH2─Cl STEP 1 Longest chain has 4 carbon atoms. C─C─C─C STEP 2 Number chain and add substituents. C ─ C ─ C ─ C ─ Cl 1 2 3 4 STEP 3 Add hydrogen to complete 4 bonds to each C. CH3─CH─CH2─CH2─Cl 2-bromo-4-chlorobutane

Constitutional Isomers Have the same molecular formula. Have different atom arrangements (different structural formula). CH3CH2CH2CH3 Butane C4H10 CH3 2-Methylpropane CH3CHCH3 C4H10

Cyclic Hydrocarbon - Cycloalkane Cyclobutane = = Cyclopentane = Cyclohexane

Physical Properties of Alkanes Nonpolar Insoluble in water. Lower density than water. Low boiling and melting points. Gases with 1-4 carbon atoms. (methane, propane, butane) Liquids with 5-17 carbon atoms. (kerosene, diesel, and jet fuels) Solids with 18 or more carbon atoms. (wax, paraffin, Vaseline)

Boiling & melting points of Alkanes Number of carbon atoms ↑ bp & mp ↑ Number of branches ↑ bp & mp ↓ CH3 CH3CH2CH2CH3 CH3CHCH3

Chemical reactions of Alkanes Low reactivity 1- Combustion: Alkanes react with oxygen. CO2, H2O, and energy are produced. Alkane + O2 CO2 + H2O + heat CH4 + 2O2 CO2 + 2H2O + energy

Halogenation Free Radical reaction 1/1/2019 Dr Seemal Jelani Chem-160

Chemical reactions of Alkanes Low reactivity 2- Halogenation: Alkanes react with Halogens. CH4 + Cl2 CH3Cl + HCl Chloromethane Heat or light Dichloromethane CH3Cl+ Cl2 CH2Cl2 + HCl Heat or light CH2Cl2+ Cl2 CHCl3 + HCl Trichloromethane Heat or light CHCl3+ Cl2 CCl4 + HCl Tetrachloromethane Heat or light

Product is hydrocarbon derivative Reaction between a substance and a halogen in which one or more halogens atoms are incorporated into molecules of the substance Product is hydrocarbon derivative Halogenation is an example of Substitution reaction It is a reaction in which part of a small reacting molecule replaces an atom or group of atoms on a hydrocarbons 1/1/2019 Dr Seemal Jelani Chem-160

General reaction heat or R-H + X2 R-X + H-X light R= Alkyl group Halogenation means: X2 where X = F, Br, Cl, I 1/1/2019 Dr Seemal Jelani Chem-160

Radical Halogenation Terms Mechanism How the reaction occurs through multiple steps (most reactions actually occur in many steps) Chain Reaction Reactions that occur on their own after some initiating event Free Radicals Atoms that have one free electron—highly reactive 1/1/2019 Dr Seemal Jelani Chem-160

Radical Halogenation Terms Initiation Step Step where a bond is split by heat/light, producing free radicals Propagation Step Step where free radicals react with non-radicals, producing more free radicals and continuing the “chain reaction” Termination Step Step where free radicals react with each other, producing non-radicals and terminating the “chain reaction” 1/1/2019 Dr Seemal Jelani Chem-160

Initiation​ ​Reaction starts with one ​photon of light.​ Must be UV​ Wavelength less than ​400nm​ Energy less than 300kJ ​per mole​ Reaction proceeds to ​completion after this. Reason is the chlorine ​molecule​ Light breaks the Cl-Cl ​bond​•​Homolytic fission​ ​Each atom takes an ​electron Forms radicals. 1/1/2019 Dr Seemal Jelani Chem-160

Initiation ​Homolytic fission forms radicals​ Radicals are very reactive atoms or groups. Cl​2​ ​2Cl​. Radicals react quickly with surrounding molecules. 1/1/2019 Dr Seemal Jelani Chem-160

Radical Halogenation of Alkanes Reactions of Alkanes Radical Halogenation of Alkanes CH4 + Cl2  CH3Cl + HCl Mechanism (chain reaction): Step 1 Cl2 ⇌ Cl· + Cl · Step 2 Cl· + CH4  CH3· + HCl Step 3 CH3· + Cl2  CH3Cl + Cl· Step 4 Cl· + Cl·  Cl2 Type of Step h Initiation Propagation Termination (Free Radicals) Overall reaction: CH4 + Cl2  CH3Cl + HCl  chloromethane Why not 1-chloromethane? Halogenated product is a haloalkane Naming: halogen atom is a substituent, replace –ine ending with –o -F fluoro -Cl chloro -Br bromo -I iodo 1/1/2019 Dr Seemal Jelani Chem-160

CHLORINATION OF METHANE Further propagation If excess chlorine is present, further substitution takes place The equations show the propagation steps for the formation of... dichloromethane Cl• + CH3Cl ——> CH2Cl• + HCl Cl2 + CH2Cl• ——> CH2Cl2 + Cl• trichloromethane Cl• + CH2Cl2 ——> CHCl2• + HCl Cl2 + CHCl2• ——> CHCl3 + Cl• tetrachloromethane Cl• + CHCl3 ——> CCl3• + HCl Cl2 + CCl3• ——> CCl4 + Cl• Mixtures Because of the many possible reactions there will be a mixture of products. Individual haloalkanes can be separated by fractional distillation. 1/1/2019 Dr Seemal Jelani Chem-160

CATALYTIC CRACKING Converts heavy fractions into higher value products Involves the breaking of C-C bonds in alkanes Converts heavy fractions into higher value products THERMAL proceeds via a free radical mechanism CATALYTIC proceeds via a carbocation (carbonium ion) mechanism CATALYTIC SLIGHT PRESSURE HIGH TEMPERATURE ... 450°C ZEOLITE CATALYST CARBOCATION (IONIC) MECHANISM HETEROLYTIC FISSION PRODUCES BRANCHED AND CYCLIC ALKANES, AROMATIC HYDROCARBONS USED FOR MOTOR FUELS ZEOLITES are crystalline aluminosilicates; clay like substances 1/1/2019 Dr Seemal Jelani Chem-160

At each level a mixture of compounds in a similar boiling range is taken off Rough fractions can then be distilled further to obtain narrower boiling ranges Some fractions are more important - usually the lower boiling point ones, high boiling fractions may be broken down into useful lower boiling ones - CRACKING 1/1/2019 Dr Seemal Jelani Chem-160

Sources of Alkanes Natural gas 90 to 95 percent methane 5 to 10 percent ethane, and a mixture of other low-boiling alkanes, chiefly propane, butane, and 2-methylpropane. Petroleum A thick liquid mixture of thousands of compounds, most of them hydrocarbons formed from the decomposition of marine plants and animals.

Alkenes and Alkynes

Alkenes and Alkynes Saturated compounds (alkanes): Have the maximum number of hydrogen atoms attached to each carbon atom. Unsaturated compounds: Have fewer hydrogen atoms attached to the carbon chain than alkanes. Containing double bond are alkenes. CnH2n Containing triple bonds are alkynes. CnH2n-2

Naming Alkenes & Alkynes Using the IUPAC alkane names: Alkene names change the end to -ene. Alkyne names change the end to -yne

Give the location for double and triple bond

Naming Alkenes & Alkynes CH2= CH ─ CH2─ CH3 1-butene CH3─ CH=CH─ CH3 2-butene CH3 | CH3─ CH=C─CH3 2-methyl-2-butene CH3─ CC ─ CH3 2-butyne 1 2 3 4 1 2 3 4 4 3 2 1 1 2 3 4

Naming Alkenes & Alkynes CH3─ CH2─ CC ─ CH3 2-pentyne CH3 CH3─ CH2─ C=CH ─ CH3 3-methyl-2-pentene CH2 – CH3 CH3─ CH2─ C=CH ─ CH3 3-ethyl-2-pentene 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Chemical Properties of Alkenes Addition Reactions Combustion Reactions 1/1/2019 Dr seemal Jelani

Chemical properties of Alkenes & Alkynes More reactive than Alkanes Addition of Hydrogen (Hydrogenation-Reduction) Addition of Hydrogen Halides (Hydrohalogenation) Addition of water (hydration) Addition of Bromine & Chlorine (Halogenation)

Aromatic Hydrocarbons

Aromatic Compounds Aromatic compounds contain benzene. Benzene has: 6 C atoms and 6 H atoms. Two possible ring structures.

Aromatic Compounds Arene: A compound containing one or more benzene rings. Aromatic compounds are named: With benzene as the parent chain. Name of substituent comes in front of the “benzene”. methylbenzene chlorobenzene ethylbenzene Cl CH2-CH3 CH3

Naming of Aromatic Compounds Some substituted benzenes have common names. CH3 Toluene

Naming of Aromatic Compounds When two groups are attached to benzene, the ring is numbered to give the lower numbers to the substituents. Start numbering from special name (if we have). If we do not have, number them to get the smallest set of numbers. Name them by alphabetical order. 3-methyltoluene Ortho Meta Para

Naming of Aromatic Compounds If we have three or more substituents: Start numbering from special name (if we have). If we do not have, number them to get the smallest set of numbers. Name them by alphabetical order.

Chemical properties of benzene Resonance: stable No addition reactions (almost unreactive) Halogenation Nitration Sulfonation

Chemical properties of benzene Halogenation Nitration